| Functional Details |
There are 16 different debounce times. In either debounce mode, the debounce time selected determines how fast the signal can change and still be recognized.
The two debounce modes are trigger after stable and trigger before stable. A discussion of the two modes follows.
Figure 13. Debounce model block diagram
Trigger after stable mode
In the trigger after stable mode, the output of the debounce module does not change state until a period of stability has been achieved. This means that the input has an edge, and then must be stable for a period of time equal to the debounce time.
Figure 14. Debounce module – trigger after stable mode
The following time periods (T1 through T5) pertain to Figure 14. In trigger after stable mode, the input signal to the debounce module is required to have a period of stability after an incoming edge, in order for that edge to be accepted (passed through to the counter module.) The debounce time for this example is equal to T2 and T5.
T1 – In the example above, the input signal goes high at the beginning of time period T1, but never stays high for a period of time equal to the debounce time setting (equal to T2 for this example.)
T2 – At the end of time period T2, the input signal has transitioned high and stayed there for the required amount of
T3 – During time period T3, the input signal remained steady. No change in output is seen.
T4 – During time period T4, the input signal has more disturbances and does not stabilize in any state long enough. No change in the output is seen.
T5 – At the end of time period T5, the input signal has transitioned low and stayed there for the required amount of
Trigger before stable mode
In the trigger before stable mode, the output of the debounce module immediately changes state, but will not change state again until a period of stability has passed. For this reason the mode can be used to detect glitches.
29